os.hpp has a number of dead and effectively unused methods that could be removed, including but not limited to:
os::distribute_processes
os::enable_vtime
os::vtime_enabled
os::default_file_open_flags
os::do_you_want_to_debug (!?)
os::is_debugger_attached
SuspendResume::is_suspend_request
There's also os::bind_to_processor which is only implemented on Solaris and only used by CMS if enabling a diagnostic flag (BindCMSThreadToCPU) which defaults to false, which seems like a reasonable candidate for deprecation and removal.